New challenges in the study of coastal aquifers from numerical modeling. The case of the Motril-Salobreña aquifer

Coastal aquifers are frequently complex systems with highly heterogeneous geological characteristics, specific flow patterns, presence of fluids with different densities, high risk of contamination both by salinization and by other pollutants, and highly modified by anthropic activity. Given this situation, numerical modeling becomes the most appropriate tool to determine the potential impact of global change on marine intrusion in this kind of aquifers. The mathematical models traditionally used in coastal aquifers have been those of flow and mass transport with variable density, which allow obtaining a distribution of salinities in the aquifer and reproducing the flow pattern in the area of discharge to the sea. In addition to these models, another type of numerical modeling can be applied that could also provide information on specific aspects of this type of aquifers. The study of the Motril-Salobreña coastal aquifer shows, for example, how heat transport models allow quantifying the recharge that occurs from rivers that frequently interact with coastal aquifers; as well as the age transport models provide data on the preferential groundwater circulation paths and its residence time, very relevant information in these frequently heterogeneous and anisotropic aquifers. Future challenges are directed towards determining the effects of sea level rise on marine intrusion and establishing the degree of equilibrium of the freshwater-saltwater contact with the current situation.